1. Field of the Invention
The present invention relates to an amorphous alloy, a molding die that includes the amorphous alloy and is used in a method for producing a camera lens or the like, and a method for producing an optical element with the molding die.
2. Description of the Related Art
The present invention relates to a molding die used in a method for producing an optical element such as a lens or a prism by press-molding a glass raw material.
A technique for press-molding a glass raw material, which does not require grinding and polishing processes, offers a simple manufacturing process and realizes simple and low-cost production of lenses. Therefore, the press-molding technique has recently become widely used in production of, as well as lenses, prisms and other optical elements in general.
Examples of properties required for a die material used for producing such glass optical elements by press-molding include high heat resistance, high chemical stability, a high hardness, good releasability, and good processibility.
Many types of molding dies have been proposed so far. For example, Japanese Patent Laid-Open No. 60-246230 proposes a molding die prepared by processing cemented carbide, which has high heat resistance, high oxidation resistance, and a high hardness, into a desired shape and coating the surface thereof with a precious metal having chemical stability and good releasability from a glass raw material to form a release film.
Recently, various glass materials have become widely used in optical elements in order to realize various optical designs. Some of the glass materials contain highly reactive components such as phosphorus and fluorine. Thus, better releasability has been required for the release film of the molding die in order to steadily mold such glass materials into a shape. Accordingly, International Publication No. WO2007/046437 proposes a glass-molding die including an amorphous alloy having chemical stability and good releasability.
However, a release film of the molding die described in International Publication No. WO2007/046437, despite having chemical stability, does not have a high hardness because it is provided as a layer to be cut and processed. The hardness of an amorphous Pt—Hf—Zr—Ni alloy described in International Publication No. WO2007/046437 was 12 GPa (measured with a nanoindenter produced by Agilent Technologies, Inc.).
In a glass-molding process, dust emission inevitably occurs in a molding die and in slide portions of an apparatus. The hardness of carbide used as a die material is about 13 to 18 GPa. When the hardness of a coating film of the molding die is about 12 GPa as described above, flaws often occur in the coating film due to chips such as carbide chips being pinched by the die in the molding process. When such a molding die having flaws is used for producing a glass optical element, the flaws of the molding die transfer to the glass optical element. This results in the glass optical element having a poor appearance.